1. Field of the Invention
The present invention relates to an exposure apparatus and, more particularly, to an exposure apparatus comprising two stages, which can be swapped between an alignment station and an exposure station.
2. Description of the Related Art
In recent years, to improve the processing capability of an exposure apparatus, such as a semiconductor exposure apparatus, a high-speed positioning apparatus, such as an original stage device or a substrate stage device has been under development. In this positioning apparatus, the amount of heat generated by an actuator which drives a stage increases. The temperature of the optical path of a laser interferometer to align the stage fluctuates due to this heat generation. The dimensions of members involved vary due to the heat generation as well. These phenomena degrade the position measurement accuracy, as well as the positioning accuracy.
Japanese Patent Application Laid-Open No. 2000-505958 discloses an exposure apparatus comprising two stages, which can be swapped between an exposure station and an alignment station. The exposure apparatus described in Japanese Patent Application Laid-Open No. 2000-505958 can execute an exposure process in the exposure station and an alignment measurement process in the alignment station in parallel.
In an exposure apparatus which executes an exposure process in an exposure station and an alignment measurement process in an alignment station in parallel, when temperature adjusting gas is supplied from the exposure station to the alignment station, the alignment accuracy may degrade. The same applies to a case wherein the direction in which the temperature adjusting gas is supplied is reversed.
For example, assume that temperature-adjusted gas adjusts the temperature of a stage positioned in a measurement processing area in an alignment station after adjusting the temperature of a stage positioned in an exposure processing area in an exposure station. In this case, the temperature-adjusted gas flows into the measurement processing area after removing heat in the exposure processing area. This locally generates temperature non-uniformity or a temperature gradient in the measurement processing area. Therefore, the alignment measurement accuracy degrades in response to a variation in a dimension of a wafer, a wafer chuck, or a stage in the measurement processing area, or a variation in temperature of the optical path for position measurement. As a result, the alignment accuracy degrades. If the dimension or shape of the wafer in alignment is different from that in exposure, the alignment accuracy degrades as well.